Bug in v41 and 41X emulation ?

[Ángel Martin]

I've been looking at a problem dealing with the support of upper-score characters (hex 106) by both V41 and the DM-41X. After some tiring troubleshooting I *think* I've narrowed it down to an issue with the SLSABC instruction (op code 0x3E8), which is supposed to write the 9-bit character in C.X to the rightmost position in the LCD.

The problem appears to occur when there's already one (or many) upper-score character in the rightmost position. In such an instance the real machine overwrites the upper-score(s) with the new char, effectively deleting all to its left.

However on V41 and the 41X the new char is placed to the right of the upper-score(s) instead, which - albeit may seem to be more logical - is not how the real machine does it.

You could argue that the real machine had a bug and the emulators don't; but herein lies the problem. Why does this matter? Even if the upper-scores are infrequently used they play an essential role in the HP-IL Devel and other functions with advanced use of the LCD. Not having the exact emulation (whether you like the way it worked) is a problem.

BTW the 41CL behaves exactly like the original machine, so 100% match right there. So that makes me wonder how that was achieved, considering it's the only system that got it "right"... It's probably due to the fact that it uses the Fullnut LCD, unlike the other two cases which emulate the Halfnut one.